1. Field of the Invention
The present invention relates to a vehicle-behavior detecting apparatus which calculates a variation value in a yaw moment from the difference between the yaw moment during constant-speed turning and the yaw moment during accelerated or decelerated turning, and also relates to a vehicle-behavior controlling apparatus.
2. Description of the Related Art
During constant-speed turning, a vehicle load does not shift in the longitudinal direction greatly, and a nearly constant state is kept. Therefore, a reaction force acting on a steering wheel does not vary greatly. When a driver suddenly presses down on an accelerator pedal to accelerate the vehicle, however, the vehicle load shifts backward, and a vertical load on rear wheels increases. Therefore, the vehicle exhibits an understeer. On the other hand, when the driver releases the accelerator pedal or presses down on a brake pedal to decelerate the vehicle, the vehicle load shifts forward, and the vertical load on front wheels increases. Therefore, the vehicle exhibits an oversteer.
Such an understeer or oversteer caused by operation of the accelerator pedal or the brake pedal destabilizes a posture of the vehicle. Various technologies controlling such vehicle behavior have been proposed.
For example, Japanese Unexamined Patent Application Publication No. 9-156487 discloses a technology controlling the vehicle behavior by: comparing a target yaw rate and an actual yaw rate; determining whether a running state of the vehicle is the understeer or oversteer in comparison with the target yaw rate; applying a braking force to a rear inner wheel in the case of the understeer; and applying a braking force to a front outer wheel in the case of the oversteer.
In the technology disclosed in the above related art, first, the target yaw rate is calculated, and then, the difference between the target yaw rate and the actual yaw rate detected by a yaw rate sensor is obtained. According to the difference, the braking force is feedback-controlled. Since the amount to be controlled is determined after the actual yaw rate is detected, the control tends to be late.
In addition, since the vehicle behavior is controlled by applying the braking force to a particular wheel, torque loss is large, and excellent acceleration performance cannot be obtained. Furthermore, since the vehicle-behavior control during turning is delayed, there are problems in that a critical lateral acceleration cannot be increased during accelerated turning, and a running stability is impaired during decelerated turning.